The present invention relates to a steering wheel having a rim portion, in which heat generating members that generate heat when electrified are incorporated.
When a vehicle is parked in extremely cold weather in winter, the temperature in the passenger compartment is lowered. Accordingly, the temperature of the rim portion of the steering wheel is lowered. The rim portion is also referred to as the handle portion or ring portion. When the driver gets in the vehicle in this state and starts driving, he/she needs to grip the cold rim portion. This can make the steering operation uncomfortable.
In this regard, various types of steering wheels have been developed that have a rim portion in which heat generating members that generate heat when electrified are incorporated. For example, Japanese National Phase Laid-Open Patent Publication No. 2004-520989 discloses a steering wheel in which a rim metal core, which forms the framework of the rim portion, is coated with a base material made of urethane foam or neoprene. A sheet-like heat generating member, which is silver coated fabric, is attached to the rim metal core. The sheet-like heat generating member is coated with a foam material layer of polyurethane and a cover in that order.
In the steering wheel, since the base material hinders transfer of heat generated by the sheet-like heat generating member to the rim metal core, a greater amount of heat is transferred to the surface of the rim portion, which in turn efficiently increases the temperature of the rim portion surface. Also, since the heat generated by the sheet-like heat generating member is diffused by the silver coating layer, the rim portion surface is evenly heated.
In the steering wheel disclosed in Japanese National Phase Laid-Open Patent Publication No. 2004-520989, the base material and the foam material layer have a seamless cross-sectional structure. Although the base material has uneven thickness about the rim metal core, the cross-section of the base material has an elliptic shape. The base material and the foam material layer are each formed by molding plastic using molds.
However, to make the base material and the foam material layer through molding process, two molds are required, which increases costs.